This from an article in the Canadian newspaper The Globe and Mail:
Electronic rust protectors will eat a hole through your wallet and probably won't protect your vehicle any more than it's protected already, according to the Automobile Protection Association.
Dealers charge as much as $800 for the quickly-installed device — a small box that applies a weak electric current to the metal on your vehicle — which normally retails for as low as $150, says APA president George Iny.
The consumer watchdog doesn't recommend the devices, which are based on the concept of cathodic protection used on the submerged parts of bridges and boat motors.
Those devices only work when the metal is submerged in water. While device manufacturers have plenty of anecdotal evidence from satisfied customers, Iny says he's seen no studies showing electronic rust inhibitors actually protect your car on the road.
“Your car's not usually underwater,” Iny says. “I'd like to see a technical report signed by a Canadian engineer that shows the device is effective.”
The article was in reference to a question by a Hyundai owner. Hyundai went on to comment:
Hyundai Canada spokesman Chad Heard says Hyundai dealers are independently operated businesses and are free to “offer value-added services to their customers.”
The only value add is to the dealer who uses your money to line their pockets.
This from Canada and I believe we invented rust. Better to invest in some blinker fluid as noted above.